JAMB Chemistry 2021 Paper

Concept:This molecule is an alkyne containing a carbon-carbon triple bond. Its IUPAC name is derived from the longest carbon chain that includes the triple bond.Explanation:In $\mathrm{HC \equiv CCH_3}$, the longest continuous carbon chain containing the triple bond has three carbon atoms.The parent alkane for a three-carbon chain is propane.Replacing the suffix $-ane$ with $-yne$ gives the base name propyne.Because the triple bond is terminal, its locant is 1, so the systematic IUPAC name is prop-1-yne, commonly written as propyne.Propyne is also known by the common name methylacetylene, since it is acetylene ($\mathrm{C_2H_2}$) with one hydrogen replaced by a methyl group.Acetylene has only two carbons, butanol is an alcohol, and decanoic acid is a carboxylic acid, so none of these fit the formula $\mathrm{HC \equiv CCH_3}$.Answer:The correct option is B — Methyl acetylene. (The actual IUPAC name is propyne.)